In the related art, various techniques for protecting a rider by mounting an airbag apparatus on a vehicle such as a motorcycle or the like are known. For example, in a motorcycle, a technique for deploying and inflating an airbag stored in a housing mounted to a vehicle body frame by inflation gas, thereby constraining a rider in case of front collision is known (for example, see Japanese Unexamined Patent Application Publication No. 2002-137777). In this technique, a possibility to secure a wide protection area by the airbag is proposed. However, it is necessary to increase the size of the airbag correspondingly. Therefore, constitution of an improved technique effective for constraining the rider reliably by the airbag even when the airbag is downsized to the minimum size is highly requested.